It is known in the art relating to internal combustion engines to use a positive crankcase ventilation (PCV) system to remove crankcase vapors (including unburned fuel and combustion products that leak past the piston rings, oil vapors, and other vapors present in the crankcase) from the crankcase. PCV systems recirculate crankcase vapors in lieu of exhausting the vapors to the atmosphere, thereby reducing engine emissions while also advantageously improving engine efficiency and increasing engine life. Generally, PCV systems utilize engine vacuum to draw fresh air from an engine air intake system through the crankcase. The level of engine vacuum varies with engine operating conditions (i.e., idle, acceleration, constant speed, deceleration). During periods of engine idle or deceleration, engine vacuum is high and therefore capable of producing flow rates through the PCV system that are generally at or above a flow rate necessary for sufficient crankcase ventilation. On the other hand, during periods of constant speed or acceleration, engine vacuum is low and therefore it produces lower flow rates than when the engine vacuum is high. The flow rate through the PCV system is therefore typically regulated to provide desirable flow rates at all or most of the various operating conditions.
Conventionally, there are two common methods in a PCV system of regulating flow from the crankcase to the engine air intake system, such as to the air intake manifold. One method is to use a spring-loaded PCV flow control valve while the other method is to employ a simple orifice in place of a PCV valve. A spring-loaded PCV valve opens at a predetermined pressure differential across the valve (e.g., between the crankcase and the valve outlet). When the pressure differential across the valve is greater than the pressure differential required to open the valve, the flow rate through the valve is approximately constant. While a spring-loaded PCV valve provides a generally constant flow rate above a certain pressure differential, it has a relatively higher cost than a simple orifice and can potentially generate noise at certain points of instability. On the other hand, while a simple orifice design is relatively less complex and less expensive, it provides less than ideal flow regulation for some of the range of pressure differentials present in the PCV system during engine operation. Therefore, a need exists for a PCV system that is both cost effective and able to provide a flow rate through the PCV system that is generally constant over an extended range of the pressure differentials between the crankcase and the engine air intake.